Rate of esterification is highest for the acid

Options

A. `CH_(3)(CH_(2))_(2)COOH`
B. `(CH_(3))_(2)CHCOOH`
C. `CH_(3)COOH`
D. `Cl(CH_(2))_(4)COOH`

Answer

To determine which acid has the highest rate of esterification, we need to analyze the structure of the acids provided and their electron-donating or withdrawing effects on the carbonyl carbon. Here's a step-by-step solution:

### Step 1: Understand Esterification
Esterification is a reaction between an acid and an alcohol that produces an ester and water. The reaction involves the cleavage of the hydroxyl (OH) bond from the acid, which is influenced by the electron density at the carbonyl carbon.

**Hint:** Remember that the rate of esterification is related to the electron deficiency at the carbonyl carbon.

### Step 2: Identify the Acids
Let's denote the acids provided in the question:
1. Acid A: CH3(CH2)2C(=O)OH (Butanoic acid)
2. Acid B: (CH3)2C(=O)OH (2-Methylpropanoic acid)
3. Acid C: CH3C(=O)OH (Acetic acid)
4. Acid D: CH3(CH2)3C(=O)OH (Pentanoic acid)

**Hint:** Write down the structural formulas of the acids to visualize their electron-donating or withdrawing effects.

### Step 3: Analyze Electron Effects
The rate of esterification increases with greater electron deficiency at the carbonyl carbon. Electron-donating groups (like alkyl groups) decrease the positive charge on the carbonyl carbon, making it less reactive.

- **Acid A (Butanoic acid)**: Has a butyl group which is electron-donating, reducing the electron deficiency.
- **Acid B (2-Methylpropanoic acid)**: Has two methyl groups, which also donate electrons, reducing the electron deficiency.
- **Acid C (Acetic acid)**: Has one methyl group, which has the least electron-donating effect compared to the others.
- **Acid D (Pentanoic acid)**: Has a longer alkyl chain, which donates electrons and reduces electron deficiency.

**Hint:** Compare the number of alkyl groups in each acid and their positions to determine their electron-donating effects.

### Step 4: Determine the Highest Rate of Esterification
The acid with the least electron-donating effect (or the highest electron deficiency at the carbonyl carbon) will have the highest rate of esterification.

- **Acid C (Acetic acid)** has only one methyl group, which means it has the least electron-donating effect compared to the others. Thus, it retains a higher positive charge on the carbonyl carbon, making it more reactive.

**Hint:** Focus on the acid with the least steric hindrance and electron-donating groups for the highest rate of reaction.

### Conclusion
The acid with the highest rate of esterification is **Acetic acid (Acid C)**, as it has the least electron-donating effect and thus the highest electron deficiency at the carbonyl carbon.

**Final Answer:** Acetic acid (Option C) has the highest rate of esterification.

---